Vertical synchronization
Vertical synchronization or vertical synchronization , VSync for short , is a term from computer technology . With graphics cards, vertical synchronization prevents the image data from being updated while the screen is building the image.
VSYNCand HSYNC( horizontal synchronization ) are also generally the ( English-language ) designators for the control signals for the start and end of a picture and a picture line.
Vertical synchronization
Option for modern graphics cards
The image build-up on CRT screens takes place line by line. An electron beam travels along a line and then skips through the lines. If the image data change during the image build-up, display errors , so-called glitches, can occur because the displayed image is no longer consistent. Typical glitches arise with straight edges that have rotated between the image change. They are shown kinked or offset.
With activated vertical synchronization, the graphics card waits until the moment when the electron beam jumps from bottom right to top left and only then updates the image data. This behavior is particularly easy to implement with several frame buffers . With activated vertical synchronization, the buffers are not swapped when the image has been completely calculated, but when the electron beam jumps back.
Vertical synchronization is problematic if the graphics card takes longer to compute a new image than the monitor to display. For example, if the monitor operates at a refresh rate of 60 Hz, but the graphics card can only process 50 frames per second, it is likely that 10 update cycles of the monitor will be skipped every second (no image is displayed). This can lead to optical delays. In the worst case, the graphics card calculated a new picture shortly after returning, but has to wait until the monitor has finished displaying the now outdated picture. When playing games , increasing the latency by a few milliseconds (maximum 1 frame, e.g. 16.7 ms at 60 Hz) can be relevant.
As a programming technique for VGA chips
Older VGA chips could not load new data into the graphics memory and display an image at the same time . Since the loading of new data had priority, the picture froze when new data arrived. With vertical synchronization, the image was precalculated in the main memory and only copied into the graphics memory when the electron beam of the monitor made a return jump. The programmer had to take care of the precise timing himself; the VGA chip only entered the position of the electron beam in a register .
As a control option for liquid crystal screens
In contrast to tube monitors, modern liquid crystal screens (flat screens) only use one (sometimes two) refresh rates , usually 60 Hz and 75 Hz. Therefore, graphics cards (or their drivers ) usually have an VSYNCoption today . If this is activated, the graphics processor or driver synchronizes the image with the refresh rate of the monitor, even if the graphics card could provide significantly higher image rates. This is why games and other programs that place high demands on the graphics sometimes have a parameter VSYNCthat can be activated in the options if display problems occur and is then passed on to the driver. If the graphics card is significantly faster than a game requires, vertical synchronization reduces the required power and thus the waste heat and power consumption of the graphics card.
See also
Individual evidence
... and comments:
- ↑ ... English called frame , for the "(picture) frame " ...
- ↑ Roland Oberhammer: Real-time object recognition on low power embedded systems. Grin Verlag, 2008, ISBN 978-3638916639 , p. 28